This invention relates to a composition and process for treating a metal surface to form a chromate coating.
It is an object of this invention to improve metal corrosion resistance and properties after painting by providing a coating having excellent corrosion resistance and paint base properties. The metals include, for example, iron, steel, zinc, galvanized steel plate, aluminum, magnesium, cadmium and alloys thereof.
Chromate coatings have conventionally been employed to improve the corrosion resistance of the bare metal surface and as a paint base coating for enhanced corrosion resistance on aluminum, zinc, galvanized steel plate, tin plate and the like and as a sealing, anticorrosive or coating on iron or steel pretreated with a phosphatizing solution and as an insulating or antiocorrosive coating for electrolytic iron plate. As the chromating solution, there have been employed chromic acid together with aminoalcohols, polyvalent alcohols, fatty acids and the like as a reducing agent suitable for the acid. However, such coatings have been unsuccessful because they have unsatisfactory corrosion resistance and adhesion of topcoated paints.